1. Field of the Invention
The present invention relates to thermoelectric heating and cooling devices. More particularly, the invention pertains to apparatus for overcoming thermal limitations in heating and cooling devices that utilize arrangements of Peltier elements of higher and lower power levels.
2. Description of the Prior Art
It is known that refrigerators equipped with Peltier modules are capable of also operating in the opposite sense. That is, they can also provide a heat chamber, provided that they are surrounded by a housing. In comparison with compressor devices, such refrigerators possess the great advantage that they can be electronically controlled very accurately to attain a constancy of temperature that cannot be achieved by other refrigerating techniques. Peltier heating/cooling chambers of the prior art have a disadvantage in that the adjustable temperature range is very limited and/or the outlay for the power loss "to be pumped away" is too great. The plate-shaped Peltier elements, generally connected in a cascade arrangement, cannot then be adequately protected against overheating (in particular at the edge zones). This applies both to Peltier cascades in one plane (cf. British patent application GB-A-2 241 378) and, to a greater extent, to pyramidal arrangements of a plurality of Peltier cascades (cf. DD-A-0 049 626 and U.S. patent Ser. No. 4,833,889).
The solutions disclosed by the above-cited patent publications permit only limited heating operation of the cascade arrangement of Peltier elements. This is due to the fact that overheating of a portion of the Peltier elements can easily occur. Such overheating gives rise to other disadvantages. For one, as a result of a restricted heating operation, rapid temperature changes to an upper limit are neither permissible or possible. Secondly, greater electric power is required in heating operation. On the one hand rapid wear results from soiling of the semiconductor material and, on the other hand, material stresses result from greater expansions.